1. Field of the Invention
This invention relates to a fiber treatment apparatus and more particularly to the apparatus of the type which utilizes sprayers or other applicators to treat a fiber mat and mechanisms for subsequently fiberizing the mat following such treatment.
2. General Discussion of the Background
Various devices are known in the art for treating fibers with crosslinking agents in mat form and thereafter breaking the mats into individual fibers. For example, U.S. Pat. No. 3,440,135 to Chung discloses a mechanism for applying a crosslinking agent to a cellulosic fiber mat, then passing the mat while still wet and following "aging" through a fiberizer, such as a hammermill to fiberize the mat, and drying the resulting loose fibers in a two stage dryer. The first dryer stage is at a temperature sufficient to flash water vapor from the fibers and the second dryer stage is at a temperature that effects curing of the crosslinking agent. A cyclone separator is then illustrated separating the fibers from the gas and for subsequent collection. Chung mentions the need for the "aging" step, of many hours duration, in order to reduce the level of nits in the resulting fiber product. As described below, nits are typically interbonded fibers which can interfere with product quality. Therefore, the Chung apparatus suffers from the drawback of requiring the inconvenient and costly storage of wet fiber mats (e.g. in roll form) for a substantial period of time in order to minimize nit formation.
Unfortunately, fiberization processes known in the art which employ currently available fiberizing or comminution machinery yield crosslinked fibers that have too many nits and knots to be acceptable for many uses. A probable reason is that such machinery has excess dead space where fibers are excessively pressed together and/or has localized regions of elevated temperature hot enough to cause premature curing of the crosslinking agent while fibers are in intimate contact with each other. Since fiberization is performed on a mat that is still wet with the uncured crosslinking agent, dead spaces and hot spots in the fiberizer would encourage the formation of interfiber bonds, which form nits, that virtually cannot be broken by downstream equipment.
Interfiber bonding in a conventional fiberizer apparatus can also lead to production of excessive amounts of "fines," which are undesirably short fibers due principally to fiber breakage. Crosslinking imparts substantial brittleness to cellulose fibers, which thereby exhibit limited compliance to mechanical stresses. Nits are especially susceptible to mechanical stresses because of their density which is much greater than the density of individual fibers. Excess fiber breakage and fines not only degrade absorbency but can substantially reduce the loft and resiliency of a product made from crosslinked fibers.
One approach to reducing fines is to diminish interfiber crosslinking, as in published European Patent Application Nos. 427,316 A2; 429,112 A2; 427,317 A2; and 440,472 A1, as well as in copending U.S. patent application Ser. No. 07/607,268, filed Oct. 31, 1990. A drawback to this approach is that the substantial elimination of interfiber bonds produces a web having low tensile strength. Wet laid sheets made from such fibers tend to fall apart, and are unsuitable for many industrial applications.
Yet another problem with prior processes is that output from the system is so rapid that fibers treated with the crosslinking agent do not have sufficient time to cure after they are fiberized and dried. Curing time can be increased by lengthening the conduit through which fiberized and dried material passes, but such a solution is expensive. Lengthening conduits requires a large capital investment that reduces cost efficiency.
Hence, there is a need for an apparatus that will produce treated fibers, such as intrafiber crosslinked cellulose, having a nit level lower than levels obtainable with existing equipment. There is also a need for such an apparatus that will produce fibers from a mat comprised of crosslinked cellulose while not causing significant breakage of individual fibers of the mat.
It is an object of this invention to provide such an individualized, intrafiber crosslinked cellulose web that has improved wet tensile strength.
It is another object of the invention to provide a process for producing an individualized, intrafiber crosslinked product that provides increased curing time for crosslinking to progress after the fibers are dried.
It is yet another object of the invention to provide such a process that has improved flash drying of moisture from the fibers prior to curing.
It is another object of the invention to enhance the uniformity of crosslinking agent application to a fibrous mat.
Another object of the present invention is to provide an apparatus and method for producing treated fibers, such as crosslinked cellulose fibers, with a low nit level and preferably a nit level no greater than about three.
Another object is to provide such an apparatus and method that comminutes one or ore mats of non-crosslinked cellulose fibers which have been impregnated with a crosslinking substance, where the comminution is performed before the crosslinking substance is dried and cured.
Another object is to provide such an apparatus and method that minimizes the breakage of individual fibers.
Another object is to provide such an apparatus and method that yields crosslinked fibers having substantially no knots.
It is yet another object to provide a crosslinking process that operates at a pH that is compatible with standard unmodified papermaking equipment.
Finally, it is an object of the present invention to provide a sheet having high bulk, wet resilience and good porosity into which liquid impregnants can be efficiently introduced.
These and other objects of the invention will be understood more clearly by reference to the following detailed description and drawings.